(a) Field of the Invention
This invention relates to a method and device for detecting pregnancy. More specifically, this invention concerns a simple and sensitive method and device for the detection of pregnancy in women; the method and device being especially useful for the detection of pregnancy in its very early stages.
(B) Prior Art
A simple, sensitive test for the early diagnosis of human pregnancy would be an important contribution to medicine and society. For instance, it would be advantageous in cases of unwanted pregnancies or in cases of habitual aborters who would benefit from early therapy. It would also be advantageous for the physician to have knowledge of an early pregnancy before prescribing a drug that may be teratogenic, or in those instances where a woman has unwittingly been exposed to a possibly teratogenic drug. Also, not to be overlooked, is the all important psychological factor for the woman to know for certain whether she is pregnant or not.
The most widely used pregnancy tests employed today are those based on the detection of human chorionic gonadotropin (HCG) in urine samples by immunological methods. These tests rely on the fact that HCG is the gonadotropin of pregnancy, being secreted by the chorionic tissue of the placenta in increasing amounts soon after the implantation therein of a fertilized ovum. [The peak secretion of HCG of more than 50,000 i.u. per a 24 hour collection of urine occurs between 56 and 84 days after the last menstrual period, E. H. Venning in "Text Book of Gynecologic Endocrinology," J. J. Gold, Ed., Harper and Row, New York, 1968, pp. 95- 97.] These tests are generally reliable for detecting pregnancy after about the twelfth day following a missed menstrual period (i.e., about the fortieth day of amenorrhea) giving about a 2 to 6% error when correctly performed, B. M. Hibbard, Brit. Med. J., 1, 593 (1971) and C. A. Horwitz, et al., Obstet. Gynecol., 43, 693 (1974). However, the tests cannot be relied upon prior to that time since they only can detect minimum concentrations of HCG of about 1000- 3000 m. i.u./ml. of urine. The main reason for not increasing the sensitivity of these tests is to avoid false positives resulting from substances which cross react with the HCG-antiserum, B. M. Hobson, J. Reprod. Fertil., 12, 33 (1966).
Recently, more sensitive tests have been developed. These newer tests are based on sensitive but sometimes non-specific radioimmunoassay (RIA) techniques. The non-specificity of these tests arises from the fact that they also give positive results with other gonadotropins such as human pituitary luteinizing hormone (LH), i.e., the antisera to HCG may cross react with LH. Using the non-specific RIA techniques, LH-HCG has been shown to rise sharply beginning 10 to 14 days after the mid-cycle LH peak in the first month of pregnancy. For example, see R. B. Jaffe, et al., J. Clin. Endocrinol. Metabol., 29, 1281 (1969); A. F. Parlow, et al., J. Clin. Endocrinol. Metabol., 31, 213 (1970); D. P. Goldstein, et al., Fertil, Steril., 23, 817 (1972), L. Wide, Lancet, 2, 863 (1969); and D. R. Mishell, Jr., et al., Am. J. Obstet. Gynecol., 117, 631 (1973).
A RIA also has been developed which is specific for the beta subunit of HCG. This latter test has been used to measure serum or plasma HCG by RIA in the presence of circulating LH during the same early period of pregnancy. See, for example, L. Wide, Lancet, 2, 863 (1969), T. S. Kosasa, et al., J. Clin. Endocrinol. Metabol., 36, 622 (1973); and T. S. Kosasa, et al., Obstet. Gynecol., 42, 868 (1973).
Although RIA techniques are sensitive, it will be appreciated that these methods are expensive and complex. They must be performed by highly trained personnel using isotopic material and very sophisticated equipment.
Another test is the radio-receptor assay for HCG recently developed by B. B. Saxena, et al., Science, 184, 793 (1974). Although less time-consuming than the RIA, this test also requires both special equipment and an operator with technical skills.
Another group of tests for pregnancy are the biological tests, including the well known "rabbit test." For a review on these and other tests see B. M. Hobson, cited above. It is a well known fact, however, that these biological tests are laborious and time-consuming. Furthermore, they require the maintenance of colonies of animals, the animals being subject to seasonal variations in sensitivity.
Still other pregnancy tests have been reported. These other tests depend on estimations of serum steroid levels or on the observation of withdrawal bleeding after progestogen alone or progestrogen-estrogen therapy. These tests are considered to be less reliable than other tests discussed above.
In accordance with the need for a simple and sensitive test for the detection of pregnancy, the present invention provides a method and a device for such a test based on the concept of ultrafiltration of body fluid (e.g., urine, serum or plasma) followed by immunological determination of HCG. Ultrafiltration has been used to concentrate initially high titres of "trophoblastic tumor HCG," in urine, M. L. Taymor, et al., J. Endocrinol., 36, 417 (1966) and S. Lok, Asian J. Med., 9, 319 (1973). Such tumors produce high levels of "trophoblastic HCG", much higher than those encountered in pregnancy. Taymor, et al. concentrated the high "trophoblastic titre HCG" urine in a step directed to the purification of this gonadotropin. Incidentally, these tumors occur only rarely. It should be noted that trophoblastic tumors will give a positive test in the present invention. Accordingly, in the case where the present method gives a positive test which is later shown to be false in regards to pregnancy, such HCG producing tumors should be suspected.
The present invention provides a convenient method and device for detecting pregnancy, especially in the early stages, the method being reliable and easily performed. Furthermore, the invention provides a method giving a substantial reduction in false positives and false negatives compared to prior art non-radioactive methods.